The invention relates to a housing for an electronic device in microwave technology, in particular for a radar sensor.
It is known from EP 0 685 930 A1, for example, that a radar sensor with a mount can be screwed to the exterior of a vehicle, for example in order to measure the distance to a vehicle ahead of it. This radar sensor has an oscillator, a mixer, an amplifier, and an antenna system for producing and receiving radar radiation as well as a receiver with evaluation electronics. In these known apparatuses, the components mentioned above are installed in one or more housings which are individually closed, as a rule very tightly, and then are fastened to the vehicle with suitable mounts.
For the technical circuit design of the evaluation electronics, it is intrinsically known to use multilayer printed boards which are mounted in the housing, possibly with an additionally placed evaluation board. In the mount, this apparatus is then installed in the bumper of the motor vehicle, for example. The essential size of the device in this connection is contingent upon the separate antennas for sending and receiving, which emit radiation through the bumper in the direction of interest. For space-saving reasons, the components are as a rule accommodated on the top between the antennas, but this can generate an undesirable leakage radiation. This requires the use of expensive shields, for example with foam absorbers, and results in high manufacturing costs due to the large number of parts.
In the improvement according to the invention, a housing of the type mentioned at the beginning, which is for use In microwave technology, has the advantage that the housing is comprised of three parts tightly connected to one another, which can be made of the most favorable material and in terms of design, can be each be embodied optimally in detail to the components to be disposed in them.
Particularly for sensing distances and speeds by means of microwave radar around a motor vehicle, the invention permits the production of a compact radar sensor in which the integration of antenna structures can be advantageously designed to reduce overall dimensions. The radar sensors required for this operate in a frequency band of approximately 24 GHz, offer the advantage of small antennas, and are relatively inexpensive to produce.
The housing according to the invention is advantageously comprised of a metal plate in its middle part, to which at least one circuit board can be attached. There are also recesses which, together with the at least one circuit board, form chambers into which the components of the electronic circuit can protrude. The bottom part, which is injection molded of plastic, has a connector device that can be contacted from the outside. The upper part is the plastic cover which is also injection molded and can also, together with the at least one circuit board, form chambers for electronic and/or microwave components. The encapsulation of the components according to the invention advantageously suppresses undesirable emissions of microwave radiation.
Advantageously, the middle part is provided with centering marks which engage in corresponding marks on the bottom part and on the cover during assembly and to simplify production, the middle part can also be symmetrically designed.
In order to attach circuit boards to the middle part, it can also be advantageously provided with recesses and mounting points; depending on the components required, one or two circuit boards can be provided, for example an upper and a lower one. The circuit details with the antenna structures must be placed on the upper circuit board due to the emission of microwaves. Multilayer circuit boards equipped on one or both sides, which are made of composite materials or multilayered ceramics, can be used in this connection, whose connections must be contacted, e.g. bonded, before the lower connector part is mounted onto the bottom. In another work step, the upper circuit board can be bonded; in this instance, a favorable disposition of contacts arranged in a row does not require any large travel distances.
The lower connector part of the housing according to the invention has the required number of connector contacts and a connector form adapted to the respective intended use; the connector contacts are injection molded in place and can be glued to the metal plate when being assembled with the middle part. As a result, the bottom part of the housing, which is comprised of the middle part and the lower connector part, can be closed in a watertight fashion where additional clips can produce an adjustment and can prevent a shifting before the gluing.
The cover of the housing according to the invention is designed in a particularly advantageous manner for encapsulating the individual units, such as antennas, oscillator, mixer, evaluation electronics, etc.. In the regions disposed opposite the antennas, materials are provided as so-called optical windows to improve the transmission of microwaves and in the other regions, materials are provided to absorb microwaves. Consequently, several functions are integrated into the plastic cover of the housing in a simple manner.
A first advantageous embodiment for producing these optical windows can be achieved by clipping metal structures into the corresponding chambers on the cover. In addition, a flat ceramic plate can also be affixed between the wall of the cover and the metal structures that are clipped in place.
In another advantageous embodiment, the optical windows are produced by metal grating structures that are injection molded in place. Furthermore, the optical windows can be fundamentally comprised of a ceramic plate that is metallized on one or both sides and is injection molded in place, where the outer side or both the outer and inner sides of the ceramic plate is/are injection molded into the cover. The metallizations on the ceramic plate can be connected to the ground of the circuit board by means of a metal spring.
For a suitable dimensioning of the chambers and parts of the housing according to the invention, for example at a frequency of 24 GHz, the distances and the material thicknesses are selected in multiples of a fourth of the wavelength of the microwave radiation. For example in air, the distance between the ceramic plate and the circuit board is approximately 3 mm, the thickness of a thick-layered ceramic plate is 1 mm, and the plastic is approx. 1.7 mm. The plastic coating, which can be applied to one or both sides, is also used here as an adaptation structure because of its dielectric constants. In order to use so-called superstrate effects, the distance in air must thereby be selected to be on the magnitude of xcex/2 of the microwave length, while the ceramic plate must be xcex/4 thick. Through the selection of a suitable metallization of the ceramic plate, the desired antenna characteristics can be achieved with only one patch as a power element in order to limit the size.
In an advantageous embodiment, the antennas are comprised of a number of patches, for example 2, 3, 4, or 6 of them; inwardly protruding dielectric horns can be provided as focusing devices in the optical windows above these patches. It is also advantageously possible for inwardly and/or outwardly protruding dielectric lenses to be provided as focusing devices in the optical windows.
Through the use of the above-mentioned focusing elements, circuit boards can be advantageously used which are significantly smaller than is possible in an apparatus with only one patch. The only requirement here is that the plastic of the cover be microwave permeable, as is the case, for example, with polyetherimide or comparable plastics.
After complete assembly of the individual parts of the housing, the cover is consequently also glued to the combination of the lower connector part and the metal middle part and is therefore also closed in a watertight fashion. In order to fasten the housing, for example to the bumper of a motor vehicle, a mount is provided on at least one of the three parts and is comprised of an extension, possibly with a thickening, with elements that can be screw connected or clipped in place. An extension and thickening of the middle part offers the advantage of better heat dissipation; by contrast, it is less expensive in terms of manufacturing to affix the mount to the plastic bottom part.
The pressure compensation inside the housing can be executed with conventional, known pressure compensation elements; a pressure compensation is also possible inside the connector and via the copper cores of the companion part plugged into it. The proposed housing according to the invention is suitable not only for building a radar sensor but also for building communications devices and other sensors which use microwaves in a frequency range of up to 140 GHz. The geometries of the housing simply need to be adapted to the components required and the wavelengths used.
In addition to the claims, these and other characteristics of proposed improvements of the invention can also be inferred from the specification and the drawings; the individual characteristics can be respectively produced in and of themselves or combined in the form of sub-combinations in the embodiment of the invention, can be produced in other areas, and can represent intrinsically patentable embodiments which are claimed herein.